Army_Monkey

I've been noticing quite a few questions about gearing lately, so I thought I'd throw this up here to help people out. It lists speed in each gear at different RPMs along with cruise RPM based on axle ratio and tire diameter. I only did it for the 6-speed, as that is the most prevalent trans in these trucks.
It looks complicated, but it's pretty simple once you figure it out. Compare your stock tire size with stock gearing based on speed or cruise RPM, then find the gears that most closely match it based on your new tire size.
For instance, my '10 STX came stock with 30" tires and 3.31 gears, so my cruise RPM is 1791 at 70 MPH. I went up to 33" tires, so in order to get my cruise RPM back to stock, I would upgrade to 3.73s, which would give me a cruise RPM of 1834, or only a 43 RPM difference.

HankHill

I do not think this takes into account the .61 gear Overdrive ratio on the Ecoboost. With stock 275/65-18 (32.07) at 60 mph my RPMS are 1500 exactly.

carbinereloaded

Do you have a higher res version of the file?

frankashaw

Thanks for the chart, my eyes are kinda sore now but, what I learned is that my 3.73 with 34" tires should perform similar to a truck with 3.55s and stock tires. It should be easy for the dealer to reprogram my speedo.

Army_Monkey

The cruise RPM is based on a 0.69 6th gear, I never heard anything about them altering the 6th gear ratio for the EB. Everything I've seen indicated the the 6R80 uses the same gears regardless of application. If you had the standard 3.15 rear, 265/60R18 tires (30.5" tall), and a 0.61 6th, if the torque converter was at 100% lockup, the engine would only be turning 1300 RPM at 60.
What rear gears does your truck have?
You also have to account for tire compression when loaded, so a tire that is theoretically 32" tall might have an actual rolling diameter of only 30.5-31", or possibly less.
This was also more of an indicator of what gears to look for when you go up in tire size than a 100% accurate version. It's too hard to account for anomalies like loaded rolling radius, trans and torque converter slippage, torque converter lockup, and even the trans programming for it to be exact.

I can't seem to get the resolution any higher, I wasn't sure how else to get it up here, so I made a bitmap out of the original spreadsheet and when I put it on Photobucket, this is how it looks no matter the original resolution. I can't attach it as an Excel file, and when I publish it as a PDF it exceeds the forum limit of 117KB.

HankHill

Yes I thought of that myself as well. The overall tire size is 32.07 for the Goodyear Wrangler SRA 275/65-18. I am guessing it is about 31 inches diameter loaded. I have a 3.55ls rear differential. I have a Ecoboost which according to specs shows a final 6th gear drive ratio at .61. At 60 mph I am at 1500 rpm.

truckerdude

it ain't got no .61 that was a misprint in some ford literature

HankHill

Are you sying the tech specs are wrong? Just Asking because it still stands as uncorrected.
http://media.ford.com/images/10031/2...Tech_Specs.pdf